Grease composition and bearing

ABSTRACT

A grease is provided which has an improved inflow property of the grease into a lubrication unit and has a long life when used for bearings even under a high temperature environment. 
     A grease composition comprising a base oil and a thickener, characterized in that the base oil contains an ester synthetic oil, the content of the ester synthetic oil is not less than 20% by mass of the total mass of the base oil and the thickener contains a diurea compound represented by the Formula (I):
 
R 1 —NHCONH—R 2 —NHCONH—R 3 ,  (I)
         wherein R 2  is a C 6-15  divalent aromatic hydrocarbon group, R 1  and R 3  are the same or different, and represent cyclohexyl or C 8-22  linear or branched alkyl, and the molar ratio of cyclohexyl to the total of cyclohexyl and C 8-22  linear or branched alkyl is 60 to 95%.

This application is the U.S. National Phase of International ApplicationNo. PCT/JP2007/058800, filed 24 Apr. 2007, which designated the U.S. andclaims priority to Japan Application No. 2007-079734, filed 26 Mar. 2007the entire contents of each of which are hereby incorporated byreference.

TECHNICAL FIELD

The present invention relates to a grease composition and a bearing,particularly to a grease composition suitably used for rolling bearingsfor automobile electrical equipment or auxiliaries and to rollingbearings for automobile electrical equipment or auxiliaries in which thegrease composition is filled.

BACKGROUND ART

A long lubrication life is required for a grease which lubricates aportion such as rolling bearings for automobile electrical equipment orauxiliaries, which is heated to extremely high temperatures andsubjected to extremely high speed movements. In order to provide a longlubrication life, the properties of the grease to easily flow into thelubrication unit, as well as heat-resistant property, are required. Suchan inflow property of the grease is particularly strongly required whenouter race rotation type bearings are used for the bearings, since it ismore difficult for the grease to flow into the lubrication unit, forexample due to the action of centrifugal force in the outer racerotation type bearings. On the other hand, when the inflow property istoo high, the grease is soft and leaks from the bearings, and thereforethe lubrication life becomes short. Thus, a grease which has a goodbalance between heat-resistant property and inflow property is demanded.

Examples of outer race rotating bearings for automobile electricalequipment or auxiliaries include bearings used for electromagneticclutch, intermediate pulley, idler pulley, tension pulley and the likeused for automobile air conditioners. On the other hand, examples ofinner race rotating bearings include bearings used for alternators andthe like.

The grease which has a long life when used for outer ring rotation typebearings may be used not only for the outer ring type bearings but alsofor inner race rotation type bearings since, as described above, thegrease has a good balance between heat-resistant property and inflowproperty.

Diurea greases which employ mainly a synthetic hydrocarbon oil or phenylether synthetic oil as a base oil are used as the grease used forrolling bearings for automobile electrical equipment or auxiliaries. Inmany cases, an aromatic diurea grease is used among diurea greases sinceit has an excellent high-temperature resistance. However, the lives ofthis sort of greases are not nearly satisfactory when used for outerrace rotation type bearing because of insufficient inflow property ofthe greases into the lubrication unit.

In the meantime, as an example of improving the inflow property by athickener, Patent Document 1 describes a grease composition in which thediurea compound represented by the following general formula is employedas a thickener in a base oil containing an ether synthetic oil in anamount more than 50% by mass of the base oil:R¹—NHCONH—R²—NHCONH—R³,wherein R² represents C₆₋₁₅ divalent aromatic hydrocarbon group, R¹ andR³, the same or different, represent cyclohexyl, C₇₋₁₂ cyclohexylderivative groups or C₈₋₂₀ alkyl; and the ratio of the number of molesof cyclohexyl and derivative groups thereof to the total number of molesof cyclohexyl, C₇₋₁₂ cyclohexyl derivative groups and C₈₋₂₀ alkyl is 50to 100%

However, this grease composition lacks in compatibility between the baseoil and the thickener, lacks in inflow property, and the life of thebearing is not satisfactory.

Patent Document 1 JP 2979274 B

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a grease compositionand a bearing.

Another object of the present invention is to provide a grease which hasan improved inflow property into a lubrication unit and has a long lifewhen used for bearings even under a high temperature environment.

Means for Solving the Problems

The present invention provides the following grease composition andbearings.

-   1. A grease composition comprising a base oil and a thickener,    characterized in that the base oil contains an ester synthetic oil,    the content of the ester synthetic oil is not less than 20% by mass    of the total base oil and the thickener contains a diurea compound    represented by the Formula (I):    R¹—NHCONH—R²—NHCONH—R³,  (I)

wherein R² is a C₆₋₁₅ divalent aromatic hydrocarbon group, R¹ and R³ arethe same or different, and represent cyclohexyl or C₈₋₂₂ linear orbranched alkyl and the molar ratio of cyclohexyl to the total ofcyclohexyl and C₈₋₂₂ linear or branched alkyl is 60 to 95%.

-   2. The grease composition according to the above item. 1, wherein    the ester synthetic oil is an ester synthetic oil which has three or    more ester groups in the molecule.-   3. The grease composition according to the above item 1 or 2,    wherein the ester synthetic oil is at least one selected from the    group consisting of trimethylolpropane ester oils, trimellitic acid    ester oils, pyromellitic acid ester oils, pentaerythritol ester    oils, dipentaerythritol ester oils, and complex ester oils.-   4. The grease composition according to any one of the above items 1    to 3, which is for bearings.-   5. The grease composition according to the above item 4, wherein the    bearings are rolling bearings for automobile electrical equipment or    auxiliaries.-   6. The grease composition according to the above item 5, wherein the    rolling bearings for automobile electrical equipment or auxiliaries    are outer race rotation type bearings.-   7. A bearing in which the grease composition according to any one of    the above items 1 to 6 is filled.

Effect of the Invention

The grease composition of the present invention has an improved inflowproperty into the lubrication unit, which makes the bearing life longereven under high temperature environments. Thus, it is an excellentgrease for bearings and exerts excellent effects as a grease forbearings, particularly as a grease for rolling bearings for automobileelectrical equipment or auxiliaries and more particularly as a greasefor bearings used for outer race rotating of rolling bearings forautomobile electrical equipment or auxiliaries.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

As described above, inflow property of the grease into the lubricationunit is required to obtain a long service life, and on the other hand,when the inflow property is too high, the grease is soft and leaks fromthe bearings, and therefore the life of the lubrication unit becomesshort. Thus, it is important that a grease has a good balance betweenheat-resistant property and inflow property.

The grease of the present invention is characterized in that the greasehas a balance between heat-resistant property and inflow property bycontrolling inflow property together with securing heat-resistantproperty by increasing the ratio of cyclohexyl group in theabove-described diurea compound while improving the inflow property ofthe grease by employing an ester synthetic oil which is compatible withthe thickener because the oil has a polarity.

Examples of thickeners generally used for a grease composition includemetallic soap thickeners containing Li, Na or the like; and non-soapthickeners such as benton, silica gel, diurea compounds and fluorinatedthickeners represented by polytetrafluoroethylene. Metallic soapthickeners, benton and silica gel, however, are not acceptable withrespect to the heat resistant property, that is, a bearing lubricationlife under a high temperature. Though the fluorinated thickener isacceptable with respect to the heat-resistant property, the price of thethickener is too high and lacks general versatility.

Therefore, the grease composition of the present invention ischaracterized by employing a particular diurea thickener represented bythe general formula I.

In the general formula I, the molar ratio of cyclohexyl group to thetotal of cyclohexyl group and C₈₋₂₂ linear or branched alkyl groupsrepresented by R¹ and R³ is 60 to 95%, more preferably 70 to 90%.

When the ratio is less than 60%, the grease is soft and leaks from thebearings, and therefore the life of the bearings becomes short. When theratio is more than 95%, the grease becomes hard, and the inflow propertyof the grease becomes worse, and therefore the life of the bearingsbecomes short.

Examples of the base oils which are employed in the grease compositionof the present invention include ester synthetic oils. Examples of theester synthetic oils include diester oils represented by di-2-ethylhexyladipate (DOA), di-2-ethythexylsebacate (DOS), di-isodecyl adipate (DIDA)and the like; aromatic ester oils represented by trimellitic acid esteroils and the like; and polyol ester oils represented bytrimethylolpropane ester oils, pentaerythritol ester oils and the like.

Particularly suitable are ester synthetic oils having trivalent or morethan trivalent ester groups in one molecule, such as trimethylolpropaneester oils, trimellitic acid ester oils, pyromellitic acid ester oils,pentaerythritol ester oils and dipentaerythritol ester oils; complexester oils which are synthesized from polyalcohols (such aspentaerythritol) with monovalent fatty acids (such as caprylic acid) andpolyvalent base acids (such as azelaic acid); and the like.

The ratio of ester synthetic oil to the total base oil is preferably notless than 20% by mass, more preferably not less than 50% by mass, mostpreferably 100% by mass. In order to sufficiently obtain theheat-resistant property and inflow property of the grease, not less than20% by mass of ester synthetic oil is preferably contained. This isbecause ester synthetic oils facilitate the inflow property of thegrease into the lubrication unit, since the ester synthetic oils have ahigh polarity and a high affinity for the thickener.

The base oil used for the grease of the present invention may containbase oils other than the ester synthetic oils. Examples of the otherbase oils include mineral oils and synthetic oils. Examples of thesynthetic oils include diester oils; synthetic hydrocarbon oilsrepresented by poly-α-olefin; ether synthetic oils represented byalkyldiphenyl ether; polyglycol synthetic oils represented bypolypropylene glycol; silicone synthetic oils: and fluorinated syntheticoils.

Any additives generally used for the grease composition as required maybe used for the grease composition of the present invention. Examples ofthe additives include antioxidants represented by amine antioxidants andphenol antioxidants; inorganic passivating agents such as sodiumnitrite; rust inhibitors represented by sulfonate rust inhibitor,succinic acid rust inhibitor, amine rust inhibitor, carboxylate rustinhibitor; metal corrosion inhibitors represented by benzotriazole;oiliness agents represented by fatty acid, fatty acid ester, phosphoricacid ester; antiwear agents and extreme pressure agents represented byphosphorous agents, sulfuric agents and organometallic agents; and solidlubricants represented by metal oxide salts and molybdenum disulfide.

EXAMPLES Preparation of Grease for Testing

A base grease was prepared by reacting an aromatic diisocyanate(diphenylmethane diisocyante) with a predermined amount of amines(cyclohexylamine, stearylamine, p-toluidine) in a base oil and dilutedthe resultant with a base oil to attain the worked penetration of 280.Additives are added to this grease to prepare grease compositions ofExamples 1 to 4 and Comparative Examples 1 to 4.

Content of cyclohexyl group (CH) (%)=[{(the number of moles ofcyclohexyl group)/(the number of moles of cyclohexyl group+the number ofmoles of alkyl groups)}×100]

-   Thickeners A1 to A5: cycloaliphatic/aliphatic diurea    (cyclohexylamine and/or stearylamine were used)-   Thickener B: aromatic diurea (p-toluidine was used)-   Thickener C: Li soap (lithium 12-hydroxystearate)

Base Oil

-   Ester oil A: trimethylolpropane ester oil (kinematic viscosity at    40° C.: 24.5 mm²/s)-   Ester oil B: pentaerythritol ester oil (kinematic viscosity at 40°    C.: 30.8 mm²/s)-   Ester oil C: dipentaerythritol ester oil (kinematic viscosity at 40°    C.: 209 mm²/s)-   Ester oil D: complex ester oils (kinematic viscosity at 40° C.: 102    mm²/s)-   Mineral oil: kinematic viscosity at 40° C.: 102 mm²/s-   Synthetic hydrocarbon oil: kinematic viscosity at 40° C.: 63.3 mm²/s-   Phenyl ether oil: dialkyldiphenyl ether oil (kinematic viscosity at    40° C.: 100 mm²/s)-   Additive A: amine antioxidant (alkyl diphenylamine)-   Additive B: sulfonate rust inhibitor (zinc dinonylnaphthalene    sulfonate)

Test Method for Grease Composition

-   Worked penetration (JIS K2220): all the consistencies were set at    280    Outer Race Rotating Test

Outer race rotating test which estimates the bearing life under a hightemperature was conducted. The bearing was driven under the followingconditions, and the bearing life was determined when the motorovercurrent or abnormal vibration was detected, or the temperature ofthe motor exceeded the prescribed temperature by +15° C.

Bearing type: 6203 rubber seal

Test temperature: 160° C.

Rotation rate: 16000 rpm

Test load: radial load 800 N

Bearing Lubrication Life Test (based on ASTM D3336)

Inner race rotating test which estimates the bearing life under a hightemperature was conducted. The bearing was driven under the followingconditions, and the bearing life was judged when the motor overcurrentwas detected, or the temperature of the motor exceeded the prescribedtemperature by +15° C.

Bearing type: 6204 metal seal

Test temperature: 180° C.

Rotation rate: 10000 rpm

Test load: axial load 66.7 N

Radial load 66.7 N

Overall Judgment

-   Outer Race Rotating Test qualified 500 hours or more disqualified    less than 500 hours-   Bearing Lubrication Life qualified 500 hours or more disqualified    less than 500 hours

Qualified in Both the Test: ◯, the Others: X

The results are shown in Table 1.

TABLE 1 Examples Comparative Examples Component 1 2 3 4 1 2 3 4Thickener A1 14.0 Thickener A2 14.0 Thickener A3 14.0 Thickener A4 14.014.0 Thickener A5 14.0 Thickener B 23.0 Thickener C 9.0 Ester Oil A 20.5Ester Oil B 45.1 45.1 87.0 Ester Oil C 73.8 36.9 36.9 Ester Oil D 49.28.2 73.0 Mineral Oil 8.2 Synthetic Hydrocarbon Oil 61.5 Phenyl Ether Oil32.8 73.8 Additive A 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Additive B 1.0 1.01.0 1.0 1.0 1.0 1.0 1.0 Worked Penetration 280 280 280 280 280 280 280280 CH Content in Thickener 70 75 87 90 50 90 0 0 Ester Oil Content inBase Oil 90 25 100 60 100 10 100 100 Outer Race Rotating Test (H) 520550 1020 770 300 390 240 20 Bearing Lubrication Life Test (H) 600 6101000 810 330 370 515 28 Overall Judgment ∘ ∘ ∘ ∘ x x x x

All of the results of the outer race rotating test and the bearinglubrication life test of the grease compositions of the Examples 1 to 4were more than 500 hours, in which compositions the content of thethickener represented by the general formula (I) in which thickener thecontent of cyclohexyl group (CH) was 60 to 95%, and the content of theester synthetic oil in the base oil was not less than 20% by mass basedon the total base oil. Therefore, the grease compositions are excellentin the heat-resistant property and the inflow property.

In contrast, all of the results of the outer ring rotating test, thebearing lubrication life test or both of the tests of the greasecomposition of the Comparative Example 1 in which the thickenerrepresented by the general formula (I) in which thickener the content ofcyclohexyl group (CH) is 50%, the composition of the Comparative Example2 in which the content of ester synthetic oil in the base oil is 10% bymass based on the total base oil and the composition of the ComparativeExamples 3 and 4 in which the thickener represented by the generalformula (I) in which thickener cyclohexyl group (CH) is not contained isused is less than 500 hours. Therefore, this shows that the object ofthe present invention is not attained.

What is claimed is:
 1. A grease composition comprising a base oil and athickener in the amount of 10.0 wt % to 18.0 wt % based on the totalweight of the grease composition, characterized in that the base oilcontains an ester synthetic oil and oils other than the ester syntheticoil, the ester synthetic oil is selected from the group consisting oftrimethylolpropane ester oils, pentaerythritol ester oils, anddipentaerythritol ester oils, the content of the ester synthetic oil isnot less than 20% by mass of total base oil, the oils other than theester synthetic oil is selected from the group consisting of mineraloils, synthetic hydrocarbon oils, ether synthetic oils, and combinationsthereof, and the thickener contains a diurea compound represented by theFormula (I):R¹—NHCONH—R²—NHCONH—R³,  (I) wherein R² is a diphenylmethylene group, R¹and R³ are the same or different, and represent cyclohexyl or C₈₋₂₂linear or branched alkyl and the molar ratio of cyclohexyl to the totalof cyclohexyl and C₈₋₂₂ linear or branched alkyl is 70 to 90%.
 2. Thegrease composition according to claim 1, wherein the ester synthetic oilis an ester synthetic oil which has three or more ester groups in amolecule.
 3. The grease composition according to claim 1, which is forbearings.
 4. The grease composition according to claim 3, wherein thebearings are rolling bearings for automobile electrical equipment orauxiliaries.
 5. The grease composition according to claim 4, wherein theroiling bearings for automobile electrical equipment or auxiliaries areouter race rotation type bearings.
 6. A bearing in which the greasecomposition according to claim 1 is filled.
 7. The grease compositionaccording to claim 1, wherein the amount of the thickener is about 14 wt%,
 8. The grease composition according to claim 1, wherein the greasecomposition is configured to have more than 500 hours of the bearinglife measured by the outer race rotating test and more than 500 hours ofthe bearing life measured by the bearing lubrication life test.